It is known for a fuel pumping assembly to include an electric motor and a fuel pump module supported together in a housing. The fuel pump module in such an assembly will generally include a module housing, an impeller that is driven by the electric motor and rotates within an impeller cavity formed in the module housing, and a semi-circular pumping channel including upper and lower pumping channel portions formed around a circular periphery of the impeller cavity. The impeller may include axially upper and lower impeller vanes spaced around an outer circumferential periphery of the impeller that move fluid through the upper and lower portions of the pumping channel, respectively, as the impeller rotates within the impeller cavity. The module housing will also include an inlet port and an exhaust port that may extend axially through respective lower and upper walls of the module housing and connect with respective inlet and outlet ends of the pumping channel. To improve pump efficiency and reduce power requirements, it is desirable to shape the pumping channel and the exhaust port to minimize fluid losses.
For example, European Patent Application EPO 784 158 AZ discloses an electric motor regenerative turbine fuel pump assembly that improves efficiency by shaping the exhaust port of its pump module to include an arcuate trench in an upper wall of its module housing. As shown in FIGS. 1-7, the pump module 20 has an exhaust port 22 located along a portion of a circumferential sidewall 24 of a module housing 26 of the module 20 adjacent an exit end 28 of its pumping channel 30 in which an impeller 31 is received. The exhaust port 22 also includes an opening 32 that leads from the outlet end 28 of the pumping channel 30 into the trench 33. The trench 33 is defined by a generally vertical trench end wall 34 disposed upstream from a ramp 36 that inclines from a floor 38 of the trench 33, in a downstream direction, i.e., the direction of impeller rotation, to an upper surface 40 of the module housing 26. The trench 33 is further defined by an arcuate radially inner wall 42 that stands opposite and parallel to an arcuate radially outer wall 44. A thin circumferential band of material 46 surrounds the module housing 26 and defines the outer wall 44 of the trench 33. However, the exhaust port opening 32 is disposed radially outward from the impeller 31 and the exit end 28 of the pumping channel 30. As best shown in FIGS. 6 and 7, this requires fuel exiting upper and lower portions 45, 47 of the pumping channel 30 to impact respective upper and lower channel exit end walls 48, 49 of the upper and lower portions 45, 47 of the pumping channel 30 before turning radially outward to exit through the exhaust port opening 32 resulting in fluid losses. In other words, the exit end 28 of the pumping channel 30 forms an elbow redirecting fluid flow radially outward from the channel 30 and through the exhaust port opening 32.
The exhaust port opening 32 includes a generally rectangular horizontal portion 54 defined on three sides by the trench end wall 34, the outer wall 44 and a leading or upstream edge 56 of the ramp 36. A fourth side of the horizontal portion 54 of the exhaust port opening 32 is defined by an imaginary line extending through space between respective radially inner ends of the sides defined by the trench end wall 34 and the upstream edge 56 of the ramp 36. The exhaust port opening 32 also includes a generally rectangular vertical portion 58 formed into the inner wall 42. The vertical portion 58 of the exhaust port opening 32 is positioned to allow fuel to exit directly from the upper portion 45 of the pumping channel 30 into the exhaust port trench 33. The horizontal portion 54 of the exhaust port opening 32 is formed in the floor 38 of the trench 33 to allow fuel to exit vertically upward from the lower portion 47 of the exit end 28 of the pumping channel 30 and into the trench 33. However, fuel exiting vertically through the horizontal portion 54 of the exhaust port opening 32 necessarily impinges on fuel exiting laterally from the vertical portion 58 of the exhaust port opening 32 resulting in impingement mixing at the opening and associated turbulence and fluid losses.
As best shown in FIG. 6, the exhaust port trench 33 is shaped to discharge the mixed upper and lower fuel flows up the ramp 36 and generally vertically away from the pumping module 20 into a chamber 60 of the fuel pump housing 62 that contains the electric motor. The fuel continues past the motor and out an outlet of the pump housing to supply fuel under pressure to an operating engine. The fuel pumping assembly of the Denso pump includes an electric motor (not shown) connected to and constructed to rotate the impeller.